JPH0246908B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an ultrasonic acceleration measuring device for a motion reflector;
In particular, the present invention relates to an ultrasonic acceleration measuring device for a moving reflector that detects, measures, or displays the acceleration of a moving reflector in a living body.

[Prior Art] A Doppler device is well known that measures the speed of a moving reflector by emitting pulse waves at a constant repetition frequency and receiving reflected waves from a moving reflector. It is used in ultrasonic diagnostic equipment that measures

Motion reflectors such as blood flow not only move at a constant speed, but also often have acceleration, and in particular, the acceleration of fluids such as blood is closely related to the pressure gradient acting on the fluid. This is useful information for knowing the pressure difference, and the blood flow acceleration in the living body is mainly used as important information for knowing the functions of the heart.

[Problems to be Solved by the Invention] Generally, the acceleration of a motion reflector is determined as a differential value of velocity, but in order to obtain the necessary accuracy, this velocity measurement requires averaging of multiple measurements, that is, an integral operation. It is based on Therefore, if the acceleration is determined from the velocity by a differential operation, the above-mentioned integral operation is canceled out, making it difficult to measure the acceleration with high precision.

[Object of the Invention] The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to measure and display the acceleration of a moving reflector with high precision and in real time without differentiating the velocity determined by integration. It is an object of the present invention to provide an ultrasonic acceleration measuring device for a motion reflector, which has a simple configuration.

[Means and operations for solving the problems] In order to achieve the above object, the present invention provides a complex signal converter that emits a periodic pulse modulated wave and converts a received signal from a motion reflector into a complex signal; It has a velocity calculator that calculates the velocity of the moving reflector from this complex signal, and an acceleration calculator, and the acceleration calculator calculates the acceleration of the moving reflector based on the output of the velocity calculator.

This acceleration calculator delays the speed signal output from the speed calculator by an integer multiple of one period of the received pulse using a delay line, and uses the difference calculator to output the speed signal that becomes the input signal of the delay line and the delay line. The difference between the signal and the signal is calculated, thereby obtaining the same result as the differential operation of velocity.

In other words, the difference signal between two velocity signals of a specific motion reflector with a predetermined period difference indicates the change in the velocity of the specific motion reflector, and this corresponds to the acceleration of the specific motion reflector. becomes. Therefore, the acceleration can be easily determined from the velocity value without performing a differential operation, and the acceleration can be displayed in addition to the velocity of the motion reflector.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 1 shows an embodiment in which the present invention is applied to a device that detects, measures, or displays blood flow acceleration in a living body using ultrasonic waves, and the output of an oscillator 1 that generates a stable high-frequency signal is The frequency-dividing synchronization circuit 2 outputs various synchronization signals necessary for the device, such as repetition frequency, clock pulses, combined waves, and drive pulses.

This drive pulse 100 is outputted from the drive circuit 3 and input to the probe 5 via the transmitter/receiver switch 4 as a constant repetition frequency (for example, 4kHz), where it is converted into an ultrasonic wave and an ultrasonic pulse. It is emitted into the body as a beam. The reflected waves from inside the living body are received by the probe 5 with a delay time corresponding to the distance between the probe 5 and the motion reflector, and the ultrasonic reflected waves are converted into electrical signals by the probe 5. converted. This electrical signal is input to the high frequency amplifier 6 via the transmitter/receiver switch 4 and amplified, and then becomes an output signal 101 for determining the acceleration of the motion reflector and is input to the envelope detector 7. The signal detected by the envelope detector 7 becomes a video signal, amplified by an amplifier 8, and then input to a display 9, where the cathode ray tube of the display 9 is modulated in brightness.

In addition, a synchronization signal 10 sweep synchronized with the radiation pulse
2 is output from the frequency dividing synchronization circuit 2 and sent to the sweep circuit 10.
The electron beam of the cathode ray tube is swept by the output signal of the sweep circuit 10, and a tomographic image of the living body is displayed on the display screen in B mode, or in M mode obtained by stopping the beam in a certain direction. will be displayed as . On the other hand, the other output signal of the sweep circuit 10 is input to a scan controller 11, which electronically or mechanically controls the ultrasonic beam emitted from the probe 5.

The characteristic feature of this embodiment is that the acceleration is calculated from the velocity signal of the motion reflector using an acceleration calculator with a simple configuration. The complex signal is converted into a signal, and speed calculations are performed based on this complex signal.

That is, the received high frequency signal is first input to the complex signal converter 200 to convert it into a complex signal, and the output 101 of the high frequency amplifier 6 described above is as follows.
The signal is input to two mixers 12 and 13. The spectrum of this high-frequency signal is composed of a large number of line spectra having frequencies that are integral multiples of the repetition frequency, but when the reflector is in motion, the frequency changes due to the Doppler effect, as is well known. To simplify the explanation of this frequency change, consider a line spectrum with frequency f ₀ at the center of the spectrum,
If the frequency changed by the Doppler effect is f _d and the amplitude is 1 (the same applies hereafter), then the received high frequency signal is expressed by the following equation.

cos2π(f ₀ −f _d )t...(1) As is generally known, if the angle between the direction of movement of the reflector and the direction of the radiation beam is constant, the Doppler frequency f _d is determined by the velocity v and radiation Since it is proportional to the wave frequency f ₀ , it is expressed by the following equation.

f _d =kf ₀ v (2) Here, v takes a positive value when the moving reflector moves away from the probe 5, and conversely takes a negative value when it approaches.

Equation (2) expresses the Doppler effect when there is no acceleration, and when moving with acceleration α and velocity v, Equation (2) is expressed as the following equation.

f _d = kf ₀ (v+αt/2) ...(3) A continuous wave with a frequency f ₀ that is an integral multiple of the repetition frequency is input from the frequency dividing synchronous circuit 2 as a reference wave to the other input side of the mixers 12 and 13. ing. The phases of these reference waves are signals that differ from each other by 90 degrees, and both reference waves become cos2πf ₀ t ...(4) sin2πf ₀ t ...(5), and in the mixer 12, equations (1) and (4) The product of the expressions is taken, and the output is cos2πf _d t+cos2π(2f ₀ −f _d )t (6). The output signal of this mixer 12 is input to a low-pass filter 14a, and the 2f ₀ frequency component is removed, so the output signal of this low-pass filter 14a is 1
03 becomes cos2πf _d t (7).

The same applies to the mixer 13, and the output signal 104 of the filter 14b is sin2πf _d t (8). These equations (7) and (8) are summarized as the following complex equation.

cos2πf _d t+i sin2πf _d t =x ₁ +iy ₁ =z ₁ ...(9) Here, i is a complex signal, and x ₁ and y ₁ are x ₁ = cos2πf _d t ...(10) y ₁ = sin2πf _dt ...(11).

The complex signal z ₁ obtained in the complex signal converter 200 in this way is transmitted to the A/D converters 15a and 15.
b, and is converted into a digital signal to improve calculation accuracy. The complex signal z ₁ is input to a speed calculator 201 to determine the speed.

The speed calculator 201 of the embodiment has a complex delay line 16
The complex arithmetic unit is composed of a complex arithmetic unit and an argument arithmetic unit that calculates the conjugate product of
19, 20, an adder 21, and a subtracter 22.

First, the real part x ₁ and the imaginary part y ₁ of the complex signal z ₁ are input to the complex delay lines 16a and 16b, respectively, and the signal is delayed by the repetition period T of the transmission pulse. These complex delay lines 16a and 16b are used as digital delay lines for shift registers or from writing to
A memory or the like that is read out with a period delay is used.

When the complex signal z ₁ is rewritten using equations (3), (9), (10), and (11), z ₁ = cos2πkf ₀ (vt + αt ² /2) + i sin2πkf ₀ (vt + αt ² /2) ...(12) and furthermore, z ₁ =cosφ ₁ +i sinφ ₁ =x ₁ +iy ₁ ...(13). Here, the argument angle φ ₁ of the complex signal is φ ₁ =2πkf ₀ (vt+αt ² /2) (14).

The outputs of the complex delay lines 16a and 16b are respectively
If x ₂ , y ₂ are combined into a complex signal z ₂ , then
It is expressed by the following equation as a signal delayed by a period T from the complex signal _z1 .

z ₂ = x ₂ + iy ₂ = cosφ ₂ + i sinφ ₂ ... (15) φ ₂ = 2πkf ₀ (v(t-T)+α(t-T) ² /2}
...(16) Then, the conjugate product of the complex signal z ₁ and the conjugate product signal z ₂ is determined. That is, the real part of the complex signal z ₂
x ₂ , imaginary part y ₂ are multipliers 17, 18, 19, 20
and the A/D converters 15a, 1
5b and is multiplied by the real part x ₁ and imaginary part y ₁ of the complex signal z ₁ input to these multipliers, and the multipliers 17, 18, 19, 20 respectively
Calculate x ₁ x ₂ , y ₁ y ₂ , x ₁ y ₂ , x ₂ y ₁ . The outputs of these multipliers are input to an adder 21 and a subtracter 22, and the adder 21 outputs x ₁ x ₂ + y ₁ y ₂ , and the subtracter 22 outputs x ₂ y ₁ - x. ₁ y ₂ is output.

Next, based on the outputs of the adder 21 and the subtracter 22, the argument of the conjugate product z ₁ z ₂ ^* of the complex signal z 1 and the conjugate complex signal z ₂ ^* of the complex signal z ₂ is determined by the argument calculator _. 33, and the velocity is determined from this deflection angle.
The conjugate product is represented by a complex signal z ₃ in the following equation.

z ₃ = z ₁ z ₂ ^* = (x ₁ + iy ₁ ) (x ₂ − iy ₂ ) = x ₁ x ₂ + y ₁ y ₂ + i (y ₁ x ₂ − x ₁ y ₂ ) = x ₃ + iy ₃ ... (17) Here, if we rewrite equation (17) using equations (13) and (15), the complex signal z ₃ becomes z ₃ = cosφ ₁ cosφ ₂ + sinφ ₁ sinφ ₂ + i(sinφ ₁ cosφ ₂ − cosφ ₁ sinφ ₂ ) ...(18), and further z ₃ =cos(φ ₁ −φ ₂ )+i sin(φ ₁ −φ ₂ )……(19). If we set this as z ₃ = cosφ ₃ + i sinφ ₃ = x ₃ + iy ₃ ...(20), then from equations (14) and (16), the argument of the conjugate product φ ₃
is φ ₃ =φ ₁ −φ ₂ =2πkf ₀ {vT+αTt−αT ² /2}
...(21) becomes.

The argument angle φ ₃ of the conjugate product is calculated by the argument calculator 33 based on the following equation.

φ ₃ = tan ^-1 y ₃ /x ₃ ... (22) This deflection angle φ ₃ is proportional to the velocity when α = 0, so it is the velocity signal of the motion reflector, and the acceleration is calculated based on this velocity signal. However, in the embodiment, in order to obtain a highly accurate speed signal, the adder 21
A video integrator 202, which is an averaging circuit, is connected to the output of the subtracter 22. This video integrator 202 includes adders 30a, 30b and a delay line 31.
a, 31b and weighting calculators 32a, 32b. Therefore, adders 30a, 30b
Then, the output delayed by one period and the current time input signal are added by the delay lines 31a and 31b, and the signals are averaged by repeating the operation of supplying this output to the delay lines 31a and 31b again.

When this addition is performed using a digital circuit, for example, an average value can be obtained by outputting the higher-order bits of the addition output. but,
If this operation is simply repeated, the output will increase as the number of additions increases, and will eventually reach saturation. Therefore, in the embodiment, the weighting circuits 32a, 3
2b is provided to attenuate the output and add it to the input. In other words, if the weighted attenuation amount is β, then the signal 10 cycles earlier than the current signal is β.
Since the signal is attenuated by the 10th power of , and added to the signal at the current time, the influence on the output is reduced, making it possible to perform the same averaging function as a low-pass filter or moving average circuit. Furthermore, it is also possible to change the degree of averaging by changing the weighting amount.

The argument angle φ ₃ of the conjugate product obtained in this way is
This is the speed signal shown by the above equation (21), and the acceleration can be determined from this deflection angle _φ3 . That is, the output of the argument subtractor 33 is the output of the acceleration calculator 204.
The acceleration calculator 204 includes a delay line 40 that delays the velocity signal by an integral multiple of one period, and a difference calculator 41. Then, the difference calculator 41 calculates the difference between the input signal of the delay line 40 and the output signal of the delay line 40, which is a speed signal before a predetermined period, and the output of this difference calculator takes out the change in the speed component. Therefore, the acceleration can be calculated from this.

The action of this acceleration calculator 204 is expressed by the formula:
Assuming that the delay time of the delay line 40 is equal to the pulse repetition period T, the output of the delay line 40 is expressed by the following equation.

φ ₄ =2πkf ₀ {VT+αT(t-T)−αT ² /2}
...(23) In addition, the difference calculator 41 calculates the argument angle φ ₃ −φ ₄ =φ ₅ , and from the above equations (22) and (23), the output of the difference calculator 41 is expressed by the following equation. expressed.

φ ₅ =2πkf ₀ αT ² (24) Therefore, in equation (24), since the repetition period T is constant, the acceleration α can be obtained by calculating the argument φ ₅ .

Also, since α is the following formula, the difference calculator 41 is
It is also possible to configure it with ROM and directly obtain α.

α=φ ₅ /2πkf ₀ T ² (25) In other words, in the difference calculator 41, by creating a table in which the acceleration α corresponding to the value of the argument φ ₅ is written in the ROM in advance, the deviation can be calculated. The acceleration α can be read immediately from the value of the angle φ ₅ , and the declination angle φ ₅ is measured between 0° and +180° and 0° and −180°, so the positive and negative values of the acceleration α can be read out. Identifiable.

In the embodiment, the declination signal obtained in this manner is converted into an analog signal by the D/A converter 34, and the screen of the CRT display 9 is modulated with a brightness amount proportional to the acceleration. can be displayed.

Therefore, the acceleration distribution along the radiation beam axis is M
It can be displayed as a mode image or a B-mode image. In addition, in the embodiment, the acceleration calculator 20
A switch 42 is provided on the output side of 4, so that either the acceleration signal or the speed signal can be selected and displayed. Note that the normal image signal from the amplifier 8 is input to the CRT 9, and it is possible to display both this image signal and the acceleration signal selectively or simultaneously, so that the motion of blood flow, surrounding tissue, Since it can be compared with the structure, extremely useful information for diagnosis can be provided. in this case,
This comparison can be further facilitated by displaying the acceleration signal in color using a color cathode ray tube.

Furthermore, in this embodiment, the clutter removal filter 203 is connected to the terminal shown in FIG.
It is inserted between AC and BD. That is, in general, for example, blood flow signals from a living body are mixed with reflected signal clutter from almost stationary in-vivo tissues such as blood vessel walls and heart walls, and these signals are usually stronger than reflected signals from blood flow. Therefore, it significantly interferes with blood flow measurements. Therefore, the clutter removal filter 20
If these clutters are effectively removed in step 3, the quality of the image signal can be significantly improved. As shown in FIG. 2, this clutter removal filter 203 consists of delay lines 51 and 52 having a delay time corresponding to one period T of the repetitive signal, and a difference calculator 5.
3 and 54, the difference between the current time signal and the signal one cycle before is successively taken, and the stationary reflected wave signal is removed. Furthermore, since the output of low-velocity signals, such as signals reflected from the heart wall, is small, it is possible to reduce the influence on blood flow signals.

[Effects of the Invention] As described above, according to the present invention, the declination, which is the velocity signal of the motion reflector, is determined from the Doppler received signal, and the acceleration is determined from the difference in declination between two declinations. Therefore, acceleration can be easily determined without directly differentiating the velocity signal, and since the acceleration calculator has a simple configuration such as a delay line, it is possible to obtain a simplified acceleration measuring device. .

Furthermore, since the delay time for calculating acceleration is only an integer multiple of the transmission repetition period, it is possible to measure and display the acceleration distribution in virtually real time, and it is possible to measure and display the acceleration distribution in virtually real time. Since the acceleration of a motion reflector can be continuously determined together with the velocity distribution, extremely accurate information regarding the motion reflector can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a preferred embodiment of the ultrasonic acceleration measuring device for a motion reflector according to the present invention, and FIG. 2 is a block diagram showing a clutter removal filter. DESCRIPTION OF SYMBOLS 1... Oscillator, 2... Frequency division synchronous circuit, 5... Probe, 6... High frequency amplifier, 8... Amplifier, 9...
...Indicator, 12, 13...Mixer, 14a, 14
b...Low frequency filter, 15a, 15b...A/D
Converter, 16a, 16b, 31a, 32b... complex delay line, 17, 18, 19, 20... multiplier,
21, 30a, 30b...Adder, 22...Subtractor, 33... Argument angle calculator, 40...Delay line, 41
...Difference calculator, 42...Switcher, 200...Complex signal converter, 201...Speed calculator, 202...
Video integrator as an averaging circuit, 203...clutter removal filter, 204... acceleration calculator.

Claims (1)

[Claims] 1. A complex signal converter that converts a received signal from a motion reflector obtained by emitting a pulse modulated wave with a predetermined repetition period into a complex signal, and a complex signal output from the complex converter. is input, and a complex delay line that delays this by an integral multiple of the pulse repetition period, a complex operator that calculates the conjugate product of the input signal and output signal of this complex delay line, and a polarizer that calculates the argument of this conjugate product. an angle calculator; a delay line that delays the argument signal output from the argument calculator by an integral multiple of the pulse repetition period; a difference calculator that calculates the difference between the input signal and the output signal of the delay line; What is claimed is: 1. An ultrasonic acceleration measurement device for a motion reflector, characterized in that the acceleration of the motion reflector is measured from the difference in the declination angle output from the difference calculator. 2. The ultrasonic acceleration measuring device for a motion reflector according to claim 1, wherein the velocity calculator includes an averaging circuit that averages a complex signal. 3. The apparatus according to claim 1 or 2, characterized in that the apparatus includes a clutter removal filter that inputs the complex signal output from the complex signal converter and removes unnecessary clutter signals. Acceleration measurement device. 4. In the device according to any one of claims 1, 2, and 3, the reflection of the motion reflector modulates the brightness of the cathode ray tube depending on the magnitude of the intensity or acceleration, and also provides a display that displays colors depending on the magnitude of the acceleration. An ultrasonic acceleration measuring device for a motion reflector, comprising: 5. An ultrasonic acceleration measuring device for a motion reflector according to any one of claims 1, 2, 3, and 4, characterized in that the measured velocity signal and acceleration signal are switched and displayed.